The function of a running shoe is, on the one hand, to help the act of running so that the runner progresses as economically as possible and, on the other hand, to protect the feet against stresses from running. In order to achieve these functions, various sports shoes have been developed, whose sole is formed to be flexible to reduce the stresses to the foot and to make the running more effective.
During running the muscles alternately stretch and contract. The running step consists of a flight phase and a support phase. During the flight phase the muscles are preactivated and prepare for the impact of the foot on the base, at which phase large reacting forces are directed at the base. At an impact phase the preactivated muscles are stretched (an eccentric phase) and store elastic energy in their structures, which energy can be utilised at a concentric phase that immediately follows the stretching. During a contact phase the runner produces by his/her muscle work a force (kinetic energy) that determines the direction of motion and acceleration of his/her centre of gravity at the flight phase. All the forces produced by the runner are conveyed to the base through a support surface formed by the running shoe. According to Newton's third law, a reacting force of the same amount but of the opposite direction is directed at the runner from the base. At the beginning of the impact phase this force is conveyed through the bones and tendons to the muscle-tendon complex, where it causes an increase in force production.
The running shoe plays a central role as a conveyor of force production between the running base and the runner. The geometry of the shoe and its rigidity and flexibility characteristics can affect the operation of regulatory systems that are important from the point of view of natural and economical movement. In addition, the geometry of the shoe allows directly influencing the magnitude of the lever arms and, through this, the requirements of force production.
A sole structure of a sports shoe is known from the U.S. Pat. No. 4,757,620, which sole structure comprises a cushioning and supporting structure placed between a wearing sole and an intermediate layer. This cushioning and supporting structure comprises a flexible toe portion substantially extending from a tip of the shoe to a ball area, a resilient heel portion tapering in a wedge-like manner from a rear edge of the shoe towards the forward tip of the shoe and extending at least over the heel area, and a body piece substantially extending from the rear edge of the shoe to the ball area of the foot or fitted over a zone adapted to fit against the heel and the arch of the foot above the heel portion, which body piece is substantially stiffer and harder than said heel portion and toe portion. Such a sole structure efficiently receives the impact shock directed at the runner's heel at a landing phase of the foot. At a rolling phase of the foot, the sole structure supports the arch of the foot, which reduces the stresses directed at the foot. At a take-off phase of the foot unnecessary sliding of the shoe is eliminated.
One of the functions of a running shoe is to protect the foot against erroneous postures, such as overpronation (the ankle rotating inward too much) or supination (a posture opposite to pronation). Known running shoes often use an overpronation protection that supports the foot during running. However, too much support may cause strain injuries as the support prevents the natural movement of the foot.
The object of the invention is provide an even better sole structure of a running shoe that promotes natural and economical movement and prevents the occurrence of strain injuries in advance.
In order to achieve these objects and those that come out later the sole structure according to the invention is characterised in what is presented in the characterising part of claim 1.